The present invention relates to an AlGaInP based semiconductor light emitting device having a structure in which a first cladding layer, an active layer, and a second cladding layer are sequentially laminated.
With respect to AlGaInP based semiconductor light emitting devices represented by an AlGaInP based laser diode (LD) or light emitting diode (LED), recently, those each having a wavelength band centered at a wavelength shorter than 680 nm, typically, at 650 nm or 635 nm have come to be practically used.
As one example of the above semiconductor light emitting devices, a III-V compound based semiconductor light emitting device, particularly, an AlGaInP based semiconductor laser will be described with reference to FIG. 3.
FIG. 3 is a sectional view of a semiconductor laser 120 which is one example of a related art semiconductor light emitting device. The semiconductor laser is fabricated by a MOCVD (Metal Organic Chemical Vapor Deposition) process. Referring to FIG. 3, on a substrate 1 of a first conducting type, for example, on an n-type GaAs substrate 1 are sequentially grown an n-type (first conducting type) GaAs buffer layer 2 having a thickness of 0.3 .mu.m; an n-type AlGaInP cladding layer 3 having a thickness of 1 .mu.m; an active layer 4 having a MQW (Multi-Quantum Well) structure of GaInP/AlGaInP; a p-type (second conducting type) AlGaInP cladding layer 5 having a thickness of 1 .mu.m; a p-type GaInP layer 6 having a thickness of 0.1 .mu.m; and a p-type GaAs current cap layer 7 having a thickness of 0.3 .mu.m.
The p-type AlGaInP cladding layer 5, p-type GaInP layer 6, and p-type GaAs current cap layer 7 are then selectively etched by typically photolithography, to form a mesa structure. Thereafter, an n-type GaAs current block layer 8 is grown to be laminated on both sides of the mesa structure, to form a semiconductor light emitting device 120.
With the recent extension of service environments of optical disks and the like, the semiconductor light emitting device 120 used as light sources of these optical disks and the like has been required to be improved in temperature characteristic, particularly, to be prolonged in service life under output operation of, for example, 30 mW at 80.degree. C.
To meet the above requirement, there have been proposed a method of increasing a composition ratio of Al in the p-type AlGaInP cladding layer 5 for strengthening confinement of carriers and light in the active layer 4, and a method of laminating a multi-layer thin film structure called a MQB (Multi-Quantum Barrier) at a portion adjacent to the active layer 4.
Japanese Patent Laid-open No. Hei 6-237038 has proposed a method of suppressing diffusion of p-type carriers by provision of a multi-layer film structure in which AlGaInP layers having strain and being different in composition ratio of Al are laminated.
Further, it may be considered that a Fermi level is raised by increasing a concentration of carriers in the p-type cladding layer, to thus substantially strengthen the confinement effect of the active layer 4.
The above-described methods, however, have disadvantages. The growth of the MQB or the AlGaInP multi-layer film having strain needs strict setting of a film thickness and a composition ratio, and if actual film thickness and composition ratio are offset from the setting values upon growth of the above MQB or the AlGaInP multi-layer film, characteristics of the device is rather degraded. Also, while it is easy to increase the concentration of carriers in the p-type cladding layer, if the carriers are diffused up to the active layer 4, there may occur defects acting as dark defects or luminescence centers in the active layer, as a result of which static characteristics such as operational current of the semiconductor light emitting device 120 are degraded and also the service life is shortened by progress of diffusion of the carriers due to heat generation or current-carrying.